From 13205de1693bfab92476dcdfff77e87ec46b277d Mon Sep 17 00:00:00 2001
From: Peter Willendrup <pkwi@fysik.dtu.dk>
Date: Mon, 12 Jan 2026 09:31:37 +0100
Subject: [PATCH] Fix for rare crash of ILL_IN4 / MPI (see e.g.
 https://new-nightly.mcstas.org/2026-01-06_output.html)

---
 mcstas-comps/examples/ILL/ILL_IN4/ILL_IN4.instr | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mcstas-comps/examples/ILL/ILL_IN4/ILL_IN4.instr b/mcstas-comps/examples/ILL/ILL_IN4/ILL_IN4.instr
index 2bab5ce7bd..7b7e995e6e 100644
--- a/mcstas-comps/examples/ILL/ILL_IN4/ILL_IN4.instr
+++ b/mcstas-comps/examples/ILL/ILL_IN4/ILL_IN4.instr
@@ -329,6 +329,10 @@ INITIALIZE %{
 
   #pragma acc update device( environment_thickness )
 
+  #ifdef USE_MPI
+  /* In case of MPI mode, add an MPI_Barrier to ensure no node runs on an uncompleted/non-existentt Dirac2D.sqw */
+  MPI_Barrier(MPI_COMM_WORLD);
+  #endif
 %}